Shift Work Raises Ovarian Cancer Risk

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Academic Journal
Main Category: Ovarian Cancer
Also Included In: Endocrinology;  Cancer / Oncology
Article Date: 16 Mar 2013 - 0:00 PDT



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Shift Work Raises Ovarian Cancer Risk

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Women who work shifts might have a higher risk of developing ovarian cancer, researchers from the Fred Hutchinson Cancer Research Center in Seattle, USA, reported in Occupational and Environmental Medicine.

In an Accompanying Commentary in the same journal, authors added that "owls" (night types) may be less affected by shift work than "larks"(morning types).

The researchers based their findings on 1,101 females with epithelial ovarian cancer (cancer that occurs in the cells lining the ovaries), 389 with borderline disease, who were compared to 1,832 controls (females without ovarian cancer).

The participants were aged between 35 and 74, years. The authors asked them about their working hours, as well as whether they worked night shifts.

According to IARC (International Agency for Research on Cancer), shift work disrupts the body's circadian rhythms and is a cancer-causing agent. Circadian rhythms are mental, physical and behavioral changes that occur during a 24-hour cycle in our bodies, which respond mainly to light and darkness, as well as the environment around us. Circadian rhythms are found in animals, plants and microbes. Our body-clock drives our circadian rhythms.

The authors explained, as background information, that shift work was found to be linked to a greater risk of developing breast cancer in previous studies.

The researchers found that: The contraceptive Pill usage was lower among the females with ovarian cancer, who also had fewer children, compared to the women in the control group. Having children and being on the Pill are known to reduce the risk of developing ovarian cancer.

Among all three groups of women, the stint of night shifts averaged from 2.7 to 3.5 years. Night shift workers were involved in a range of jobs, the most common being food preparation and service, office work, admin support and healthcare.

The authors reported that compared to those who worked normal office hours, working night shifts was linked to: Twenty-seven percent of the "owls" had worked night shifts, compared to 20% of those who described themselves as "larks".

The risks of any type of ovarian cancer were: The risk of borderline tumors were: The authors say these differences are "not statistically significant".

Older women (aged 50+ years) were considerably more likely to develop ovarian cancer if they had done night shifts.

The findings in this study are similar to those found in previous studies on breast cancer and shift work, the investigators wrote. However, there appeared to be no growing risk of ovarian cancer the longer a woman continued working night shifts.

Altered melatonin levels at night may impact on cancer risk

The authors suggest that melatonin, a hormone that is normally produced at night and regulates a woman's reproductive hormones, including estrogen, may play a role in increasing ovarian cancer risk among night-time shift workers.

Melatonin, which is not produced in the presence of ambient light, suppresses estrogen levels. Shift workers are exposed to ambient light.

Higher estrogen levels are associated with a higher risk of ovarian cancer.

In an Abstract in the journal, the authors concluded:

"We found evidence suggesting an association between shift work and ovarian cancer. This observation should be followed up in future studies incorporating detailed assessments of diurnal preference (ie, chronotype) in addition to detailed data on shift schedules."

Several studies have linked shift work with cancer risk, but not all



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